1. Field of the Invention
The present invention relates to a polishing machine particularly used for polishing a work piece, such as a semiconductor wafer or the like, which requires a high flatness.
2. Description of the Related Art
A conventional polishing machine comprises a turntable, a head, and a polishing agent supply device. The turntable is made of cast iron, aluminum, stainless steel or the like. An emery cloth is adhered on the surface of the turntable by an adhesive agent such as a double coated adhesive tape. The head is provided so as to oppose the turntable. A work piece is retained by the head. The polishing agent supply device supplies a polishing agent onto the emery cloth.
A work piece is polished as follows. The turntable wearing an emery cloth adhered on its surface is rotated, to supply a polishing agent onto the polishing cloth by the polishing agent supply device. Subsequently, while the work piece is rotated by the head and is simultaneously reciprocated in a radial direction of the turntable, the surface of the work piece is pressed against the emery cloth.
In this polishing machine, to finish the surface of a work piece at an excellent flatness, the flatness of the surface of the turntable naturally must be excellent. In addition, unless an emery cloth is adhered uniformly on the turntable, an excellent flatness of the surface of the work piece cannot be obtained. Further, since the emery cloth is much softer than the turntable and a strong force effects on the emery cloth when polishing the work piece, the emery cloth must be securely adhered on the turntable.
In general, an emery cloth is manufactured by subjecting an unwoven polyurethane cloth to foaming processing and buff-processing. An emery cloth is gradually abrased during polishing, and therefore, must be replaced at a predetermined operation cycle. Since a conventional polishing machine is constructed such that an emery cloth is directly adhered on a turntable, the emery cloth is manually replaced with hands, on the turntable in an operation room where the polishing machine is placed.
Therefore, a conventional polishing machine results in following problems, with respect to operations for replacing emery clothes on the turntable.
(a) Since an emery cloth is securely adhered on the surface of the turntable, the cloth cannot easily be peeled off with hands.
(b) Since a replacement of an emery cloth takes a long time for which the polishing machine must be stopped, the productivity of the machines is low.
(c) When the polishing machine is placed in an operation room on a production line for semiconductors or the like where cleanliness is required, a replacement of an emery cloth is carried out in the room. As a result, polishing agents and shavings are scattered in the room, and the cleanliness of the room is lowered.
To maintain the flatness of the surface of the turntable during polishing, the following characteristics are demanded for a turntable.
(a) Deformation is small against a pressure.
(b) Deformation caused by a heat generated during polishing is small.
To satisfy these requirements, a conventional turntable is generally made of material, e.g., cast iron, aluminum, stainless steel, or the like. Therefore, the weight of a turntable is considerably large. For example, in case of a turntable made of cast iron and having a diameter of 600 mm and a thickness of 100 mm, the weight reaches 206 kg. As a result, the entire weight of a polishing machine is extremely large.
Meanwhile, in many cases, factory buildings for manufacturing semiconductor have a plurality of floors. In second or higher floors of such buildings, normally, the withstand load is not considerably high. In these cases, it is difficult to place polishing machines on a second or higher floor, and this is one of the limitations to lay-out designs semiconductor production line.